The present invention is directed, in general, to surface acoustic wave circuits and, more specifically, to a hermetic package for a surface acoustic wave (SAW) device and a method of manufacturing the package.
Electronic signal processing by means of surface acoustic wave (SAW) devices has been widely adopted by the electronics industry. Such SAW devices can be designed to operate as analog electrical filters that operate at over a wide range of frequencies and have several advantages over conventional technologies. One such advantage is that they can be designed to provide complex signal processing in a single unit. SAW devices also benefit from the ability to be mass produced using semiconductor microfabrication techniques which produces highly uniform devices at a substantially reduced cost. SAW devices can be easily integrated into many digital communications systems and designed to operate in high harmonic modes in the gigahertz (GHz)frequency range.
The response characteristics of a particular SAW device are governed by several factors. One is the geometry of conductors laid out on the SAW resonator""s piezoelectric substrate. A typical geometry for a SAW resonator includes first and second SAW finger sets. Portions of the finger sets are interdigitated in a central region of the SAW resonator and are employed to generate or attenuate acoustic waves. Additional non-interdigitated finger sets lie outside of the central region and serve to reflect acoustic waves back into the central region. Proper operation and containment of the acoustic waves require precise construction of both the central and outlying regions.
The interdigitated finger sets act as input and output signal ports when an AC voltage is applied to the signal input portion of the metal lines. Application of an appropriate input electrical AC signal provides the stimulus to create an acoustic wave that may typically be a Rayleigh wave with motion confined to about one acoustic wavelength under the free surface of the piezoelectric substrate. Alternatively, the acoustic excitation may be a xe2x80x9cleaky wave,xe2x80x9d which also finds application in modern radio frequency devices. This wave is propagates to the receiver portion. The fingers corresponding to the signal receiving portion draw energy from the acoustic wave in the lattice and convert it into a filtered electrical signal.
Conventional SAW devices include a device substrate and a mounting substrate sandwiching the SAW circuit, the device and mounting substrates having similar footprints. The similarity of the footprints conceals the contact pads on the mounting surface of the device substrate, thereby necessitating the use of vias. The vias are drilled through the device substrate and/or the mounting substrate to expose portions of the contact or bond pads sandwiched between the substrates and subsequently filled with metal. The vias thereby provide conduction paths from the sandwiched SAW circuit bond pads to circuit contacts on the outer surface of the SAW device. The necessity of such vias is an undesirable effect of the similarity of the footprints of the device and mounting substrates. Incorporating the vias requires additional manufacturing steps and materials, thereby increasing the production time and costs associated with each SAW unit. Use of the vias also limits the number of connection configurations employable in subsequent circuit integration.
Accordingly, what is needed in the art is a surface acoustic wave device and a method of manufacturing a surface acoustic wave device that provides improved access to SAW circuit contacts while maintaining or improving device production time and costs.
To address the above-discussed deficiencies of the prior art, the present invention provides a hermetic package for an electronic device and methods of manufacturing one or more of such packages. In one embodiment, the package includes: (1) a device substrate having: (1a) an active region containing an electrically conductive pattern that constitutes at least a portion of the device, (1b) a contact region surrounding the active region and containing bond pads that are electrically coupled to the conductive pattern and (1c) a bonding region surrounding the active region, (2) a non-porous mounting substrate having a bonding region thereon and a footprint smaller than a footprint of the device substrate and (3) a bonding agent, located between the bonding region of the device substrate and the bonding region of the mounting substrate, that bonds the device substrate to the mounting substrate to enclose the active region proximate a void between the device substrate and the mounting substrate, the contact region remaining exposed.
The present invention therefore introduces the broad concept of hermetically packaging an electronic device while leaving its bond pads exposed. This eliminates the need for further routing of conductors within the package.
In one embodiment of the present invention, the active region is sunken into the device substrate relative to the bonding region thereof to accommodate at least a portion of the void. In an alternative embodiment, a central region of the mounting substrate is sunken into the mounting substrate relative to the bonding region thereof to accommodate at least a portion of the void. In another alternative embodiment, both the device and mounting substrates have sunken portions that together accommodate the void. In another embodiment, a recess in the bonding agent accommodates the void, the recess corresponding to the active region.
In one embodiment of the present invention, the contact region is exposed to allow the bond pads to be used for wire bonding. In an alternative embodiment, one or more of the bond pads have a vertical conductor formed thereon, wherein the vertical conductor may be a stud bump. Of course, other methods of electrically coupling the packaged device to surrounding circuitry are within the broad scope of the present invention.
In one embodiment of the present invention, the device substrate includes at least one selected from the group consisting of: (1) bismuth germanium oxide, (2) gallium arsenide, (3) lithium borate, (4) lithium niobate, (5) lithium tantalate, (6) langasite, (7) lead zirconium tantalate and (8) quartz. Those skilled in the art will understand, however, that other materials may be suitable for use as a device substrate, depending upon the particular application involved.
In one embodiment of the present invention, the mounting substrate includes at least one selected from the group consisting of: (1) ceramic and (2) silicon. Those skilled in the art will understand, however, that other materials may be suitable for use as a mounting substrate, depending upon the particular application involved.
In one embodiment of the present invention, the device is selected from the group consisting of: (1) a surface acoustic wave device, (2) a micro-electromechanical system device, (3) a mirror device and (4) a piezoelectric device. Those skilled in the art will understand, however, that other devices are within the broad scope of the present invention.
In one embodiment of the present invention, the footprint of the mounting substrate is a quadrilateral. Of course, other footprint shapes are within the broad scope of the present invention. For example, the footprint of the mounting substrate may have an irregular shape that exposes only the portions of the contact region that contain the bond pads.
In one embodiment of the device, the package further includes a carrier substrate coupled to the device substrate or mounting substrate. Those skilled in the art will understand how such a carrier substrate may be used to comply with industry standard mounting footprints which may differ from a footprint of the mounting substrate.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.